Subdivisions of the turtle Pseudemys scripta subpallium based on the expression of regulatory genes and neuronal markers.

The patterns of distribution of a set of conserved brain developmental regulatory transcription factors and neuronal markers were analyzed in the subpallium of the juvenile turtle, Pseudemys scripta. Immunohistochemical techniques were used with a combination of primary antibodies for the identification of the main boundaries and subdivisions in the basal telencephalon. In the basal ganglia, the combinatorial expression on Pax6, Nkx2.1, and GABA was a powerful tool for the identification of the nucleus accumbens, the dorsal portion of the striatum, and the pallidal regions. It was also possible to suggest migratory streams of neurons from the pallidum into the striatal regions. On the basis of GABA, Pax6, Tbr1, tyrosine hydroxylase, Darpp32, and Nkx2.1 combinatorial expression patterns, the boundaries of the septal subdivisions and their embryological origin were assessed. In particular, the bed nucleus of the stria terminalis was identified. Within the amygdaloid complex, the striatal central amygdala was characterized by Pax6 expression, whereas Orthopedia gene expression highlighted, at least, a subdivision of the medial amygdala. A newly identified preoptic commissural area and the boundaries of the preoptic area were assessed, mainly by the localization of Nkx2.1 expression. Finally, additional data were obtained by combining immunohistochemistry and tracing techniques on the interneuronal nature of the cholinerginergic, nitrergic, and Nkx2.1-positive striatal cells. Taken together, all the results of the present study allowed recognizing main features in the organization of the subpallium in reptiles that, in most cases, are shared with other amniotes and amphibians.